Enhanced VWF clearance in low VWF pathogenesis: limitations of the VWFpp/VWF:Ag ratio and clinical significance

Abstract

Increased von Willebrand factor (VWF) clearance plays a key role in the pathogenesis of type 1 and type 2 von Willebrand disease (VWD). However, the pathological mechanisms involved in patients with mild to moderate reductions in plasma VWF:Ag (range, 30-50 IU/dL; low VWF) remain poorly understood. In this study, we investigated the hypothesis that enhanced VWF clearance may contribute to the pathobiology of low VWF. Patients with low VWF were recruited to the LoVIC study after ethics approval and receipt of informed consent. Desmopressin was administered IV in 75 patients, and blood samples were drawn at baseline and at the 1-hour and 4-hour time points. As defined by recent ASH/ISTH/NHF/WFH guidelines, 20% of our low-VWF cohort demonstrated significantly enhanced VWF clearance. Importantly, from a clinical perspective, this enhanced VWF clearance was seen after desmopressin infusion, but did not affect the steady-state VWF propeptide (VWFpp)-to-VWF antigen (VWF:Ag) ratio (VWFpp/VWF:Ag) in most cases. The discrepancy between the VWFpp/VWF:Ag ratio and desmopressin fall-off rates in patients with mild quantitative VWD may have reflected alteration in VWFpp clearance kinetics. Finally, bleeding scores were significantly lower in patients with low VWF with enhanced VWF clearance, compared with those in whom reduced VWF biosynthesis represented the principle pathogenic mechanism. This trial was registered at http://www.clinicaltrials.gov as #NCT03167320.

Conflict of interest statement

Conflict-of-interest disclosure: J.S.O. has served on the speaker’s bureau for Baxter, Bayer, Novo Nordisk, Boehringer Ingelheim, Leo Pharma, Takeda, and Octapharma and on the advisory boards of Baxter, Bayer, Octapharma CSL Behring, Daiichi Sankyo, Boehringer Ingelheim, Takeda, and Pfizer; and has received research grants from Baxter, Bayer, Pfizer, Shire, Takeda, and Novo Nordisk. M.L has served as a consultant for Sobi and CSL Behring and has received indirect funding for development of educational content from Takeda. J.M.O. has received research grant funding from LEO Pharma and Grifols. P.J. has received research funding from CSL Behring, Takeda, and Bayer. The remaining authors declare no competing financial interests.

A complete list of the members of the Zimmerman Program Investigators appears in the “Appendix.”

© 2023 by The American Society of Hematology. Licensed under Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International (CC BY-NC-ND 4.0), permitting only noncommercial, nonderivative use with attribution. All other rights reserved.

Figures

Figure 1.

Enhanced clearance plays an important role in the pathogenesis of low VWF. (A) VWF:Ag fall-off (decrease in VWF:Ag from T+1 to T+4 hours after desmopressin infusion, as a percentage of T+1) is illustrated on the y-axis. The red dotted line and shaded area illustrate the ASH/ISTH/NHF/WFH guideline threshold of >30% for enhanced clearance. (B) Plasma VWF:Ag levels at 1 hour and 4 hours after desmopressin treatment in patients with low VWF with FC compared with patients with low VWF with NC rates. (C) Patients with low VWF with FC had a significantly greater increment in plasma VWF:Ag levels at 1 hour after desmopressin (median, 3.84-fold vs 2.89-fold; P < .0001). The increment is expressed as fold change (T+1/T0). Similarly, patients with low VWF with FC demonstrated significantly greater increments in plasma VWF:RCo (D) (median, 4.66-fold vs 3.60-fold; P < .0001) and plasma FVIII:C levels (E) (median, 3.40-fold vs 2.81-fold; P < .01) at 1 hour after desmopressin infusion. (F-H) Conversely, patients with low VWF with FC demonstrated greater fall-offs in plasma VWF:Ag, VWF:RCo, and FVIII:C levels between 1 hour and 4 hours after desmopressin. All fall-off values are expressed as fold change between the 1-hour and 4-hour time points. (I-J) In patients with low VWF, fall-off rates in plasma VWF:Ag levels after desmopressin treatment correlated significantly with fall-off rates in both VWF:RCo and FVIII:C (Pearson’s r), consistent with faster clearance of the VWF-FVIII complex from the circulation. Median values are illustrated by black lines. ∗P < .05; ∗∗P < .01; ∗∗∗P < .001; ∗∗∗∗P < .0001. ns, not significant.

Figure 2.

Limitations of VWFpp/VWF:Ag ratio in detection of fast VWF clearance in patients with low VWF and the impact of clearance on bleeding phenotype. (A) Only 8% (6 of 75) of patients with low VWF had VWFpp/VWF:Ag ratios >3 (above the dashed blue line). In contrast, 20% (15 of 75) of the patients with low VWF had enhanced clearance based on fall-off rates after desmopressin (to the right of the dashed red line: shaded area with >30% fall-off in VWF:Ag levels at 4 hours, per ASH/ISTH/NHF/WFH guidelines). The blue line illustrates VWFpp/VWF:Ag ratio >3. Patients with low VWF with suspected enhanced clearance, as defined by VWFpp/VWF:Ag >3 only are shown in the blue box. Patients with low VWF with confirmed enhanced clearance after desmopressin trial only are shown in the light red box. Finally, patients with low VWF with both positive VWFpp/VWF:Ag and enhanced clearance after desmopressin are in the purple box. (B) Because the majority of patients with low VWF were of blood group O (64 of 75; 85.3%), the VWFpp/VWF:Ag vs desmopressin fall-off comparison was repeated with a blood group O–specific VWFpp/VWF:Ag cutoff of >2.15 (corresponds to lower 97.5% CI for normal subjects in blood group O). Even with this lower cutoff, only 12% (9 of 75) of patients with low VWF had an elevated VWFpp/VWF:Ag ratio. (C) In patients with low VWF, 24 hour fall-off in plasma VWF:Ag levels (n = 24) strongly correlated with 4-hour fall-off of VWF:Ag levels (Spearman’s r). The 24-hour fall-off is expressed as fold change (T+24/T+1−1). (D) Conversely, there was no correlation between the 24-hour fall-off in VWF:Ag and steady-state plasma VWFpp/VWF:Ag ratios (Spearman’s r). (E-F) Elimination half-lives (t1/2el in hours) in patients with low VWF correlated inversely with the 4-hour fall-off plasma VWF:Ag levels after desmopressin (Pearson’s r) but did not correlate with VWFpp/VWF:Ag ratios (Spearman’s r). (G) Patients with low VWF with a threefold or higher increment in plasma VWF:Ag levels after desmopressin (illustrated as fold change, T+1/T+0) had significantly lower bleeding scores than patients with low VWF with attenuated desmopressin responses (median, 4 vs 6; P < .01). The upper limit of the normal condensed MCMDM-1 VWD score range is illustrated by the black dotted line (<3 for both males and females). (H) Increment in plasma VWF:Ag levels after desmopressin was significantly associated with the condensed MCMDM-1 VWD bleeding score. (C-H) Fast clearance, red dots; normal clearance, blue dots.